Regulation of magnetic electron multipliers



Sept. 13, 1938. T. B. PERKINS REGULATION OF MAGNETIC ELECTRON MULTIPLIERS Filed May 18, 1957 INVENTOR 'THEODORE B. PERKINS ATTORNEY Patented Sept. 13, 1938 UNITED STATES REGULATION OF MAGNETIC ELECTRON MULTIPLIERS Theodore B. Perkins, Bloomfield, N. J.,

assignor,

by mesne assignments, to Radio Corporation of America,

a corporation of Delaware Application May 18, 1937, Serial No. 143,2s'i

6 Claims.

My invention relates to electron multipliers, and more particularly to automatic regulation of magnetic type electron multipliers to obtain stability of operation and substantially constant output when such multipliers are operated from a voltage supply, such as a commercial circuit, subject to minor variations in voltage. Magnetic electron multipliers, such as the electron multiplier disclosed in U. S. patent to Malter 2,073,599, March 9, 1937, have between an electron source and an output electrode a number of secondary electron emitters to which the electron discharge is directed in succession by crossed electrostatic and magnetic fields. In conventional operation the strength of the magnetic field is constant, but the intensity of the electrostatic field is dependent uponthe supply voltage. To focus the multiplier and obtain maximum output the strength of the magnetic field is adjusted to bring it into proper relation to the intensity of the electrostatic field at normal operating voltage. As this relation is rather critical, the multiplier is very sensitive to voltage variation on any of the electrodes, and minor variations in voltage, such as are apt to appear on the usual commercial circuits, may change the intensity of the electrostatic field to such an extent that the relation between the two fields changes to such an extent that the multiplier is out of focus and a considerable change in the output current occurs. When stable operation of a magnetic multiplier operated from a commercial circuit is necessary, it has heretofore been customary to supply the multiplier with a substantially constant supply voltage obtained from the commercial circuit by a special power pack capable of delivering a well regulated voltage or current at high values. Such special power packs are so costly that operation of magnetic multipliers from commercial circuits has not been commercially feasible.

The principal object of my invention is to regulate a magnetic multiplier automatically to obtain stable operation and substantially constant output when the multiplier is operated from a commercial circuit or similar source of voltage subject to minor variations, for example, those within a range of about 10% above and below the normal voltage. A further object is to provide a self-contained magnetic electron multiplier which will give a substantially constant output when its two supply terminals are connected directly to a power pack of the conventional type. To this end the magnetic field of the multiplier is made to vary proportionally with changes in intensity of the electrostatic field and to compensate for the effects 01' such changes in intensity. For example, this compensation may be obtained by connecting a coil which determines the'strength of the magnetic field to 5 the same power supply which generates the voltage for the electrostatic field so that variations in the power supply voltage will afiect both the electrostatic and the magnetic fields proportionally. The coil may, for example, be connected with a voltage divider which furnishes the voltage to the multiplier electrodes. With such a connection, and the two fields adjusted to produce maximum output at the lowest voltage to which the power supply is expected to vary, it will be found that when the normal operating voltage is midway between the extremes of voltage variation, a minor increase for example in supply voltage which tends to increase the multiplier output because of the increase in intensity of the electrostatic field, also tends to decrease the multiplier output because of the increase in strength of the magneticfield. As a result, the output from the multiplier will remain substantially constant in spite of the minor increase in supply voltage. Since the variations simultaneously produced in the intensity of the electrostatic field and in the strength of the magnetic field by variations in the power supply voltage have opposite eifects on the output current, those effects can be made tocounteract each other so nearlythat the output current is constant.

For a better understanding of the invention, together with other and further objects and advantages, reference may be made to the accompanying drawing in which one form of magnetic electron multiplier constructed in accordance with my invention is shown diagrammatically.

The electron multiplier shown in the drawing comprises an elongated highly evacuated envelope I, having near one end an electron source such as a photo-cathode 2 exposed to a modulated light beam indicated by the dotted line arrows, and having near the other end an output anode 3 connected to a load or output circuit. A number of secondary electron emitters 4 arranged in a row between the electrons source and the output anode so as to be struck in succession by the electron discharge from the electron source to the output anode are connected to the source 50 of supply voltage. These emitters are preferably fiat metal plates treated with some material such as caesium oxide to give them a high ratio of secondary electron emissivity. A row of acceleratingelectrodes 5 opposite the emitters v4 are also 55 connected to the source of supply voltage and produce an electrostatic field which tends to draw electrons away from each emitter.

The electron discharge in the tube is constrained to follow an arcuate or trochoidal path from the electron source to each secondary emitter in succession and thence to the output electrode by a magnetic field which is substantially homogeneous throughout the length of the tube and which extends across the electrostatic field parallel to the surfaces of the emitters 4. This magnetic field is preferably produced by a magnet having a core with elongated pole pieces 6 extending lengthwise and on opposite sides of the tube, the strength of the magnetc field between the pole pieces being determined by an exciting coil I which surrounds a portion of the core of the magnet. The emitters are maintained at successively higher positive potentials with reference to the electron source, and the accelerating electrodes are impressed with potentials sufficient to produce electrostatic fields of the desired intensity by voltages derived from a suitable voltage source, preferably a voltage divider comprising a resistor 8 connected to and in series with the exciting coil 1 of the magnet so that both the electrostatic field and the magnetic field vary with changes in supply voltage. The series connection is conveniently made by connecting one end of the coil 1 to the adjacent end of the resistor 8, the other ends of the coil and of the resistor being connected to the supply terminals 8 and H). To permit initial adjustment of the strength of the magnetic field, an adjusting resistance ll may be connected in shunt with the exciting coil 1. The coil 1 may be connected in other obvious ways as long as both the voltage derived from the voltage divider and the current through the coil vary proportionally and with changes in supply voltage.

A conventional power pack for supplying voltage to the terminals 9 and i0 is diagrammatically indicated in the drawing as a rectifier l2 supplied from a transformer l3, which is connected to a commercial supply circuit l4 subject to the usual minor voltage variations.

In operation, the strength of the magnetic field is adjusted by the adjusting resistance H to have such relation to the intensity of the electrostatic field that maximum output of the multiplier is obtained at the lowest voltage which will appear between the terminals 9 and I0 as a result of minor voltage variations on the supply circuit. With this adjustment, and at normal operating voltage, which is midway between the extremes of minor voltage variations on the supply circuit, the multiplier is slightly out of focus, the electrostatic field being slightly below and the magnetic field being slightly above the necessary values to produce focus, and the sensitivity of. the multiplier is slightly less than the maximum. Under these conditions, it will be found that the proportional changes in the electrostatic and the magnetic fields due to minor variations in the normal operating voltage are such that a voltage decrease tends to bring the multiplier into focus, where the output per volt is a maximum, and a voltage increase tends to put the multiplier still more out of focus, with a corresponding decrease in output per volt. These changes in focus with corresponding changes in sensitivity produced by minor voltage variations bear such a relation to the changes in supply voltage which produce the changes in focus that the output remains approximately constant in spite of minor voltage variations. For example, it has been found that after proper adjustments were made. the overall electrostatic voltage on a nine stage magnetic multiplier could be varied from 1000 volts to- 1200 volts, with a corresponding variation in current through the exciting coil of the electromagnet of from 59 m. a. to 71 m. a., while the output current was constant at 1.3 m. a.

I claim:

1. The method of regulating the output current of a magnetic electron multiplier in which an electrostatic field of an intensity dependent on supply voltage and a magnetic field across said electrostatic field constrains an electron discharge to impinge on a secondary electron emitter, which consists in changing the strength of the magnetic field in response to changes in the supply voltage to maintain the strength of. the magnetic field proportional to the intensity of the electrostatic field for minor variations in the supply voltage.

2. The method of neutralizing the effect of minor variations in operating voltage on the output current of a magnetic electron multiplier in which an electron discharge is directed to a secondary electron emitter by crossed electrostatic and magnetic fields which consists in counteracting the effect on the electron discharge of changes in intensity of the electrostatic field due to variations in supply voltage by producing in response to said variations corresponding and proportional changes in the strength of the magnetic field.

3. The method 0! obtaining a substantially constant output current from a magnetic electron multiplier dependent on crossed electrostatic and magnetic fields and operated from a voltage supply subject to minor variations which consists in increasing and decreasing the strength of the magnetic field in response to minor variations in supply voltage and simultaneously with and in proportion to increases and decreases in the intensity of the electrostatic field due to minor increases and decreases in the supply voltage. I

4. A magnetic electron multiplier comprising a secondary electron emitter, an accelerating eletcrode for producing an electrostatic field to draw electrons away from said emitter, a resistor having a point intermediate its ends connected to said accelerating electrode, and a ma net having an exciting coil with one end connected to an adjoining end of said resistor for producing across said electrostatic field a magnetic field which varies in strength with variation in voltage between the other ends of. said coil and said resistor.

5. A magnetic electron multiplier comprising a secondary electron emitter, an accelerating electrode spaced from and opposite to said emitter, a source of distributed voltage having an intermediate point connected to said accelerating electrode to produce an electrostatic field to draw electrons away from said emitter, and a magnet for producing across said electrostatic field a homogeneous magnetic field parallel to said emitter and having an exciting coil connected to said source to render the strength of the magnetic field dependent on the voltage of said source and proportional to the strength of said electrostatic field.

6. A magnetic electron multiplier having electrodes including an electron source, an output anode, a secondary electron emitter, and an accelerating electrode, said emitter and said soin series with said resistor foriproducing between said emitter and said accelerating electrode a. magnetic field parallel to said emitter and transverse to the path of discharge from said source to said anode and responsive to' variations in 5 potential impressed on said resistor.

THEODORE B. PERKINS. 

